272 research outputs found

### Quasinormal modes and Stability Analysis for 4-dimensional Lifshitz Black Hole

We study the Lifshitz black hole in 4-dimensions with dynamical exponent z=2
and we calculate analytically the quasinormal modes of scalar perturbations.
These quasinormal modes allows to study the stability of the Lifshitz black
hole and we have obtained that Lifshitz black hole is stable.Comment: 7 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1205.058

### Solitons in Five Dimensional Minimal Supergravity: Local Charge, Exotic Ergoregions, and Violations of the BPS Bound

We describe a number of striking features of a class of smooth solitons in
gauged and ungauged minimal supergravity in five dimensions. The solitons are
globally asymptotically flat or asymptotically AdS without any Kaluza-Klein
directions but contain a minimal sphere formed when a cycle pinches off in the
interior of the spacetime. The solutions carry a local magnetic charge and many
have rather unusual ergosurfaces. Perhaps most strikingly, many of the solitons
have more electric charge or, in the asymptotically AdS case, more electric
charge and angular momentum than is allowed by the usual BPS bound. We comment
on, but do not resolve, the new puzzle this raises for AdS/CFT.Comment: 60 pages, 12 figures, 3 table

### Current practice in methodology and reporting of the sample size calculation in randomised trials of hip and knee osteoarthritis: a protocol for a systematic review

Background
A key aspect of the design of randomised controlled trials (RCTs) is determining the sample size. It is important that the trial sample size is appropriately calculated. The required sample size will differ by clinical area, for instance, due to the prevalence of the condition and the choice of primary outcome. Additionally, it will depend upon the choice of target difference assumed in the calculation. Focussing upon the hip and knee osteoarthritis population, this study aims to systematically review how the trial size was determined for trials of osteoarthritis, on what basis, and how well these aspects are reported.
Methods
Several electronic databases (Medline, Cochrane library, CINAHL, EMBASE, PsycINFO, PEDro and AMED) will be searched to identify articles on RCTs of hip and knee osteoarthritis published in 2016. Articles will be screened for eligibility and data extracted independently by two reviewers. Data will be extracted on study characteristics (design, population, intervention and control treatments), primary outcome, chosen sample size and justification, parameters used to calculate the sample size (including treatment effect in control arm, level of variability in primary outcome, loss to follow-up rates). Data will be summarised across the studies using appropriate summary statistics (e.g. n and %, median and interquartile range). The proportion of studies which report each key component of the sample size calculation will be presented. The reproducibility of the sample size calculation will be tested.
Discussion
The findings of this systematic review will summarise the current practice for sample size calculation in trials of hip and knee osteoarthritis. It will also provide evidence on the completeness of the reporting of the sample size calculation, reproducibility of the chosen sample size and the basis for the values used in the calculation.
Trial registration
As this review was not eligible to be registered on PROSPERO, the summary information was uploaded to Figshare to make it publicly accessible in order to avoid unnecessary duplication amongst other benefits (https://doi.org/10.6084/m9.figshare.5009027.v1); Registered January 17, 2017

### Charged Randall-Sundrum black holes and N=4 super Yang-Mills in AdS(2)xS(2)

We obtain some exact results for black holes in the Randall-Sundrum model
with a single brane. We consider an extreme black hole charged with respect to
a Maxwell field on the brane. The near-horizon geometry is determined. The
induced metric on the brane and the black hole entropy are compared with the
predictions of 4d General Relativity. There is good agreement for large black
holes, with calculable subleading corrections. As a separate application, the
bulk solution provides a gravitational dual for (strongly coupled, large N) N=4
SYM in AdS(2)xS(2) for arbitrary relative size of AdS(2) and S(2).Comment: 13 page

### Large N Field Theory and AdS Tachyons

In non-supersymmetric orbifolds of N =4 super Yang-Mills, conformal
invariance is broken by the logarithmic running of double-trace operators -- a
leading effect at large N. A tachyonic instability in AdS_5 has been proposed
as the bulk dual of double-trace running. In this paper we make this
correspondence more precise. By standard field theory methods, we show that the
double-trace beta function is quadratic in the coupling, to all orders in
planar perturbation theory. Tuning the double-trace coupling to its (complex)
fixed point, we find conformal dimensions of the form 2 + i b, as formally
expected for operators dual to bulk scalars that violate the stability bound.
We also show that conformal invariance is broken in perturbation theory if and
only if dynamical symmetry breaking occurs. Our analysis is applicable to a
general large N field theory with vanishing single-trace beta functions.Comment: 26 pages, 6 figures. v3: small changes, version published on JHEP

### Black strings with negative cosmological constant: inclusion of electric charge and rotation

We generalize the vacuum static black strings with negative cosmological
constant recently discussed in literature, by including an electromagnetic
field. These higher-dimensional configurations have no dependence on the
`compact' extra dimension, and their boundary topology is the product of time
and $S^{d-3}\times S^1$ or $H^{d-3}\times S^1$. Rotating generalizations of the
even dimensional black string configurations are considered as well. Different
from the static, neutral case, no regular limit is found for a vanishing event
horizon radius. We explore numerically the general properties of such solutions
and, using a counterterm prescription, we compute their conserved charges and
discuss their thermodynamics. We find that the thermodynamics of the black
strings follows the pattern of the corresponding black hole solutions in AdS
backgrounds.Comment: 35 pages, 8 figures, final versio

### Sequences of dipole black rings and Kaluza-Klein bubbles

We construct new exact solutions to 5D Einstein-Maxwell equations describing
sequences of Kaluza-Klein bubbles and dipole black rings. The solutions are
generated by 2-soliton transformations from vacuum black ring - bubble
sequences. The properties of the solutions are investigated. We also derive the
Smarr-like relations and the mass and tension first laws in the general case
for such configurations of Kaluza-Klein bubbles and dipole black rings. The
novel moment is the appearance of the magnetic flux in the Smarr-like relations
and the first laws.Comment: 26 pages, 1 figur

### Charged-rotating black holes and black strings in higher dimensional Einstein-Maxwell theory with a positive cosmological constant

We present arguments for the existence of charged, rotating black holes in
$d=2N+1$ dimensions, with $d\geq 5$ with a positive cosmological constant.
These solutions posses both, a regular horizon and a cosmological horizon of
spherical topology and have $N$ equal-magnitude angular momenta. They approach
asymptotically the de Sitter spacetime background. The counterpart equations
for $d=2N+2$ are investigated, by assuming that the fields are independant of
the extra dimension $y$, leading to black strings solutions. These solutions
are regular at the event horizon. The asymptotic form of the metric is not the
de Sitter form and exhibit a naked singularity at finite proper distance.Comment: 21 pages, 9 figure

### Evolution of floral symmetry

Flowers can be classified into two basic types according to their symmetry: regular flowers have more than one plane of symmetry and irregular flowers have only a single plane of symmetry. The irregular condition is thought to have evolved many times independently from the regular one: most commonly through the appearance of asymmetry along the dorso-ventral axis of the flower. In most cases, the irregular condition is associated with a particular type of inflorescence architecture. To understand the molecular mechanism and evolutionary origin of irregular flowers, we have been investigating genes controlling asymmetry in Antirrhinum. Several mutations have been described in Antirrhinum, a species with irregular flowers, that reduce or eliminate asymmetry along the dorso-ventral axis. We describe the nature of these mutations and how they may be used to analyse the molecular mechanisms underlying floral evolution

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